The invention relates to a radar system comprising a transmitter having a periodically tunable HF-transmitter tube, as a magnetron with rotating tuning body, and a modulator adapted to trigger the transmitter tube for generation and transmission of a radar pulse, the frequency of which can vary in dependence upon the position of the triggering moment relative to the tuning curve produced by the periodic tuning, and a receiver with a local oscillator the output signal of which is mixed with echo pulses caused by the transmitted radar pulses for transforming these echo pulses to an intermediate frequency, the local oscillator operating at a frequency which can be controlled by means of a control signal and being included in a slave control circuit, in which the local oscillator in the interval before triggering of the transmitter tube is slaved to the transmitter tube, so that its frequency follows the variations in the turning frequency of the transmitter tube, while upon triggering the local oscillator is locked to a frequency value which produces the desired intermediate frequency with the transmitted radar pulse.
Such a system is suitable for transmission of radar pulses having randomly varying frequency, because, if the transmitter tube is triggered with a pulse signal which is independent of the periodic tuning, the transmitted pulses will have a frequency which varies randomly from pulse to pulse (jumping frequency mode).
However, in certain applications it is desirable to be able to bring such a radar system with a transmitter tube of this kind to operate is a mode with predicted transmitter frequency. In case of a magnetron with rotating tuning body it has previously been proposed for this purpose to reverse the tuning body and lock the body in a given angular position corresponding to the predicted frequency by means of a mechanical locking device. This solution has the drawback that it requires a special locking mechanism and that the switching from jumping frequency to predicted frequency will require a substantial time period.